This invention relates to the manufacture of flexible rubber tubing with annular or helical corrugations. More particularly, the invention relates to an unique variation of the method and apparatus for the manufacture of such tubing in accordance with U.S. Pat. Nos. 3,168,604; 3,304,581; 3,669,586; 3,705,780; 3,975,129; 4,053,275; 4,113,828; 4,308,228; and/or 4,360,493, and especially to a method and apparatus that produces tubing with a plurality of axially spaced corrugated length portions. For the purpose of this specification, the expression "circumferential" with respect to convolutions and corrugations will be used to include both annular and helical convolutions and/or corrugations.
As disclosed in the above patents which are incorporated by reference herein, corrugated tubing with annular or helical corrugations may be made with external forming devices including axially spaced annular disks or helices that are employed with forming mandrels and air pressure systems to produce embryonic corrugations in uncured rubber sleeves. Each time a tube is formed, the external forming device is placed over a forming mandrel (coated with a lubricant such as a silicone composition) on which a sleeve of uncured rubber has been positioned and the sleeve is radially expanded so that it bulges into the spaces between the disks or turns of the helices to form creases between the bulges.
According to the aforesaid patents, the external forming member and sleeve are then collapsed axially so that the sleeve is axially compressed, concertina fashion. The creases, together with adjacent bulges provide embryonic corrugations.
Then the forming member is axially extended together with the sleeve so that the sleeve may be removed from the forming mandrel and from within the forming member. The uncured rubber sleeve is then placed on a cylindrical curing mandrel where it is axially foreshortened, concertina fashion into a corrugated form with a desired spacing between adjacent annular or helical corrugations. The curing mandrel with the sleeve on it is then placed in an oven to cure the sleeve and set the corrugations.
The method and apparatus thus described have been used to produce flexible tubing of both circular and non-circular cross-sectional form with either annular or helical corrugations. Such tubing is used to great advantage in many and various applications.
In some applications, it may be desired to have a length of tubing that includes uncorrugated axial length portions, as well as a plurality of corrugated length portions spaced apart from one another by the uncorrugated length portions. With this arrangement, corrugated portions may be located where angular bends are to be formed in the conduit provided by the tubing. The corrugations are not required in linearly extending portions of the conduit.
In the past, tubing having these axially spaced corrugated length portions has been made by using multiple forming devices positioned during manufacture at axially spaced length portions of the uncured rubber sleeve where corrugations are desired. This can be a complicated process and can require several workers in order to position and manipulate the forming devices and to axially compress and expand the forming members during the forming of the embryonic corrugations.
The method of the present invention, however, resolves the difficulties indicated above and affords other features and advantages heretofore not obtainable.